This invention relates generally to vehicle moisture detection systems which detect precipitation on an outer surface of a vehicle window or windshield and, more particularly, to a rain detector which is decoupled from the windshield and capable of separately detecting both rain on an exterior surface and fog on an interior surface of the window.
Several rain sensor systems have been proposed. Early attempts were typically closely coupled to the interior surface of the windshield, such as by bonding to the glass surface or the like. The problem with such closely coupled units is that they create difficulty in the necessity to handle two different windshield configurations in the factory, which increases inventory costs. Also, the close coupling creates a difficulty in the replacement of the windshield in the after market. This is a result from the necessity to replace the rain sensor on the windshield after the windshield has been replaced. The other difficulty with closely coupled rain sensor units is that the close proximity of the units to the glass surface results in a relatively small sampling area. Therefore, in order to achieve an adequate sampling area, closely coupled units increase the number of sampling channels which results in the increase of cost and bulk to the unit.
In order to avoid concerns with replacing a windshield as it may become broken or cracked, and other deficiencies with units coupled to the windshield, other devices have been proposed that are decoupled from the windshield such that the sensor is spaced from the interior surface of the windshield. However, such a system is not good at determining when the signal it receives is due to rain droplets on the exterior of the windshield or due to fog particles on the interior surface of the windshield. Therefore, fog on the inside of the windshield may result in a false rain signal to the system, which may lead to the windshield wipers being turned on when there is no moisture present on the exterior surface of the windshield.
Other systems have been proposed to decouple the rain sensor from the windshield in order to overcome some of the disadvantages of previously proposed systems. One such device orients an illumination source and an illumination sensor at an acute angle relative one another such that when the light is redirected by fog droplets on the inner surface of windshield, it is not received by the sensor, while light that is refracted through the windshield and further reflected by water droplets on the exterior surface of the windshield may be received by the sensor, thereby supposedly detecting rain droplets on the exterior surface of the windshield. While such a device may arguably reduce the likelihood of a false signal of rain when there is only fog present on the interior surface of the windshield, the device does not determine that fog is present on the interior surface. Therefore, such a device has not been proposed for use with a blower or ventilation system of the vehicle to activate the blower and eliminate the fog as it becomes present on the interior surface of the windshield.
Another proposal in which the rain sensor is decoupled from the windshield is disclosed in an international patent application to Dennis Hegyi, published Nov. 24, 1994, under international publication number WO 94/27262. Although the device disclosed in Hegyi overcomes some of the difficulties of the prior art, it is not without its own difficulties. Hegyi recognizes that having the unit spaced from the windshield again allows inner surface interference, such as from fog or other moisture collecting on the inner surface of the windshield, as well as from cabin smoke and the like coming between the sensor and windshield. Although Hegyi purports to discriminate rain on the exterior of the windshield and fog on the interior of the windshield, the results have not been totally satisfactory. The Hegyi unit is an integrating sensor which integrates the output of a photo detector over time in order to attempt to detect either rain on the exterior of the windshield or fog on the interior of the windshield. Such an integrating sensor tends to dilute the impact of any individual phenomena, such as a raindrop or a particle of fog, thereby reducing the ability to detect such phenomena.
Typically, the illumination sources implemented in these rain sensors are LEDs or laser diodes, which project an infrared signal toward the windshield. Due to the wavelengths of the infrared signals, the signals are substantially invisible to a human eye and transmit readily through a standard vehicle windshield. However, vehicle manufacturers have developed filter characteristics within certain windows and windshields that substantially reduce the amount of near infrared light that may transmit through the glass and into the vehicle, thereby avoiding solar loading within the vehicle by infrared radiation radiating from the sun. While these filter characteristics are generally inefficient and allow a range of near infrared wavelengths in the proximity of visible light to transmit therethrough, they substantially hinder the effectiveness of a typical infrared emitting LED implemented in a conventional rain sensor.
The present invention is intended to provide a vehicular rain sensor which accurately detects rain on the windshield under a wide variety of operating conditions, including the presence of fog on the windshield interior, and provides the ability to separately detect the presence of rain or fog on a window of a vehicle.
According to an aspect of the invention, a rain sensor which senses rain and/or fog on a vehicle window includes an imaging array sensor directed toward a vehicle window and a control which responds to an output of the imaging array sensor in order to indicate precipitation on an exterior surface of the window.
According to another aspect of the invention, the control may include a computer programmed with an edge detection algorithm, for detecting the edges of droplets of rain as they appear on the exterior surface of the windshield. The control may be coupled to a windshield wiper such that the wipers are turned on when a predetermined threshold value of precipitation is detected on the window. An illumination source may also be implemented for illuminating the window when ambient light levels are low.
According to another aspect of the invention, an optic may be included between the imaging array sensor and the windshield. The optic has a low f-ratio which provides a narrow depth of field to the imaging array sensor, such that only the area immediately adjacent the windshield is in focus on the imaging array sensor. The imaging array sensor and optic are oriented relative the windshield to satisfy the Scheimpflug condition such that the optic focuses an entire sampling area of the windshield onto the correspondingly angled imaging array sensor.
According to another aspect of the invention, the vehicle rain sensor includes a polarizing filter that is at least occasionally positioned in an optical path between the illumination source and the sensor to filter out polarized light radiated from a fog particle on the inside of the window. The control responds to a signal from the sensor in order to indicate precipitation on an exterior surface of the window independent of moisture on an interior surface of the window.
According to still yet another aspect of the present invention, a vehicle rain sensor for detecting rain or fog on a vehicle window comprises at least one illumination source and at least one illumination sensor, having at least one optic path therebetween. At least one of the optic paths is defined between at least one of the illumination sources and the vehicle window, and between the vehicle window and at least one of the illumination sensors. A polarizing filter is positioned along at least one of the optic paths, and a control responds to an output of at least one of the illumination sensors in order to indicate precipitation on an exterior surface of the window or fog on an interior surface of the window. The control may communicate with the vehicle windshield wipers and/or the rear window wipers when rain is detected on the exterior surface of the window and communicate with a blower within the vehicle to activate the blower when fog is detected on the interior surface of the window.
The invention provides a new principle of rain detection which is decoupled from the windshield and accurately detects the presence of rain on the windshield and distinguishes rain from other phenomena which could be confused with rain, such as fog. The invention further accurately provides for the separate detection of fog, thereby allowing further measures to be taken to improve driver visibility.
These and other object, advantages and features of this invention will become apparent upon review of the following specification in conjunction with the drawings.